What Polymer Clay Is

January 12th, 2010

For those unfamiliar with polymer clay, I’d like to offer a some basic information about what the substance actually is.

However, it is almost more definitive to talk about what it is NOT. Polymer clay is NOT the same as the clays used to make pottery, ceramics, and other traditional clay items. It is NOT a clay that comes from the earth, as traditional clays do. Polymer clay is, in a word, plastic. However, that is too simple. Plastics have evolved enormously in recent decades and there are many different levels of plastic. From “cheap” plastics, that dollar store items are made from, to the super plastics used in medicine and space exploration, one can no longer equate the word plastic with something that is low-quality, unreliable and worthless.

Because polymer clay is NOT a traditional earth-based clay, it is no surprise that it is used for completely different applications than traditional clays. Polymer clay is used to make miniatures, doll sculptures, jewelry, and for covering an endless list of objects. It is also used like very thick paint to create three dimensional painting. Polymer clay is often used to create components of a larger piece of art, such as mosaics or parts or assemblages.

There are several different brands of polymer clay, the best known being Fimo and Sculpey. Polymer clay is the generic name that is used in the industry. Many lay people only know it as “Fimo” and don’t realize that polymer clay and Fimo are one and the same.

Using and Uses

Polymer clay fires at a much lower temperature than traditional earthen clays and a kiln is not needed. The average firing temperature (we also call it “curing”) is about 270 degrees Fahrenheit, so it can be cured in a typical home oven. (Always follow the safety instructions!)

Another aspect that makes polymer clay very different from traditional clay, is its ability to pick up and hold impressions of the most minute details. It will pick up the texture, lines and detail of whatever presses against it, which includes finger prints, the weave of fabrics, or the veins of a leaf.

When cured, the strength and hardness of polymer clay varies from brand to brand. It is also much more expensive than earthen clays by the pound. Because of these two factors, polymer clay is usually not used to create whole vessels out of, such as bowls, vases, cups, etc. The brands of clay that are stronger when cured, tend to also be flexible and a bit soft to the touch. The brands that are harder and more rigid, when cured, tend to be brittle.

Because of this, polymer clay artists frequently use a solid base material, and cover it with clay design and sculpture. Glass is a popular material to cover, as is metal and wood, which are a little harder to work with. Popular materials to cover are glass, ceramic greenware, wood, and metal. There are special and different techniques used for each different type of base material. Wood is one of the more difficult substrates to work with.

The Toxicity Controversy

Beginning in 2008, nearly all of the manufacturers changed the formulation of their clays to remove the small amounts of PVC used, because of controversy about its toxicity. Eberhard Faber, the maker of Fimo, was the first to do so and required to do so by changing European laws. The major American manufacturers followed suit voluntarily.

There have been many questions and discussions about the toxicity of polymer clay. There is a lot of misinformation out there on this subject, and much of it is based on older versions of polymer clay and other molding materials, that are the predecessors to polymer clay. As of 2010, the polymer clay brands are all rated as non-toxic art materials.

Polymer clay is not recommended for use on the parts of containers that will have food in contact with them, not because of toxicity of the clay itself, but because it is slightly porous. It is thought that minute particles of food and foodbourne bacteria could become trapped in the pores and contaminate the item for further food use. This has not been proved or disproved by research, as yet, however it is the reason it is not recommended for use for food items.

It is also important to avoid burning polymer clay in an unventilated area. Like all burning plastics, the fumes are considered not healthy. The max temperature varies from brand to brand, but most will burn at above 300 F. Frequent curing of many polymer clay pieces in an oven will build up a residue on the interior of the oven. It is thought that, after a large residue buildup, using the oven at a much higher temperature (like, for food) will cause toxic fumes to form. Again, this is one that has not been put to the test of research.

Polymer clay artists that do frequent curing of large quantities, often use a dedicated oven. If they use a regular kitchen oven, they put the polymer clay pieces inside another container, such as two large aluminum roasting pans, one for the bottom and the other for the lid.

For those inquiring minds, who want to know more, technical-type information, there is a wealth of information available on the internet, and a search with any good search engine yield many resource to read. There is also a large amount of misinformation out there, so be careful.. Of particular value, the information in the Wikipedia is excellent.